Parasitic infections caused by flatworms (platyhelminths) are neglected diseases and a major cause of disability, mortality and significant economic losses in many developing countries. Large-scale treatment of flatworm infections relies on a single drug available: praziquantel, and the emergence of drug resistance is an impending menace. The identification of novel drugs, in particular if they target the parasite by a different mechanism, is an important goal in public health in the poorest regions and countries. We have demonstrated that the redox homeostasis and antioxidant defenses of platyhelminth parasites are fully dependent on a single enzyme, thioredoxin glutathione reductase (TGR). This biochemical scenario differs from that of the host where there are related but distinct pathways. Recent studies in schistosomiasis validated TGR as a novel rational drug target, and have shown that oxadiazole N-oxides offer great promise as new drug leads for schistosomiasis. In this project, we will identify effective and specific inhibitors of platyhelminth TGRs, selectively disturbing flatworm redox homeostasis. In comparative enzymatic inhibition assays we will use: i) a panel of recombinant TGRs from tapeworms and flukes (the two major groups of platyhelminth parasites) as well as human recombinant thioredoxin reductases and TGR, and ii) a panel of oxadiazole N-oxides and gold coordination compounds already identified as inhibitors of Echinococcus granulosus TGR. We will assess the effect of best inhibitors (i) in vitro using cultured parasites; and (ii) in vivo in rodent models. For best inhibitors the mechanism of inhibition will be characterized. Series expansion will be carried out based on the results obtained and in silico docking and neural network predictions. In addition, we will further investigate catalysis and regulation of platyhelminth TGRs. We will study: i) the mechanism of glutathione reduction, ii) deglutathionylation activity of flatworm TGRs, and iii) the role of regulatory cysteine(s) in TGR. These biochemical studies will assist in drug optimization and design. The project addresses a significant global health problem, with high relevance to Uruguay and other countries. PUBLIC HEALTH RELEVANCE: Neglected tropical diseases caused by flatworm infections are associated with high morbidity and mortality and constitute a heavy burden to poor countries. Large-scale treatment of these infections relies on a single drug and there is justified concern regarding the emergence of drug-resistant parasites, and a pressing need for new drugs. We propose a straightforward approach to treat flatworm infections by identifying drugs selectively interfering with the redox homeostasis of the parasites.